1. Field of the Invention
The invention relates to a hydrocyclone apparatus for separating the constituents of a mixed phase input stream, such as, for example, separation of two immiscible liquids. Separation is effected by reason of the difference of the specific gravities of the constituents, which are subjected to centrifugal force as the stream is directed along a helical path between an inlet and outlets.
2. Description of Prior Art
Hydrocyclones are well known in the art. See, for example, U.S. Pat. No. 6,019,825 issued Feb. 1, 2000 to the assignee of this application and the disclosure of which is incorporated herein by reference. Numerous patents relating to hydrocyclones are listed on said patent.
In general, a hydrocyclone comprises a chamber which, for example, can be formed by a pair of concentric spaced walls which are long relative to their diameters, and each of which can be of the same diameter along its length or of decreasing diameter in the direction from the top inlet and to the bottom heavy liquid outlet end of the chamber. A mixed stream, e.g. consisting of heavy, or high density, liquid and a light, or low density liquid, is directed into the chamber, near or at the top of the chamber, at very high velocity and follows a helical path from the point at which the stream enters the chamber to the lower end of the chamber. The helical path flow can be augmented by a helical vane or tube between the chamber walls. The stream constituents are subjected to centrifugal force as they traverse the helical path so that the heavier constituents move outwardly toward the outer wall and the lighter constituents migrate toward the inner wall.
There comes a time in the pumping of many oil wells when the liquid in the well is much less than 50% oil, the remainder being mainly water or brine. Thus, the liquid may contain 5% oil and 95% brine. Under the latter conditions, it can be uneconomical to process the liquid above ground, i.e. to provide a hydrocyclone separator above ground and to pump the liquid from the liquid pool thousands of feet below ground to the hydrocyclone above ground. In addition, the separated liquid and solids, other than the oil, must be disposed of which involves further expense, particularly because of ecological restrictions with respect to disposing of such liquids and solids.
Therefore, it can be desirable to treat the low oil content liquid with a hydrocyclone disposed below ground in the bore of the well pipe because when the hydrocyclone is so located, it is unnecessary to pump the entire untreated liquid to the surface of the ground and the undesired liquids and solids can merely be returned to the liquid pool at the bottom of the well pipe.
However, the bore of the well pipe may be only about five inches in diameter which limits the maximum exterior dimensions of the hydrocyclone and the connections thereto. Thus, if the connections, e.g. pipe fittings, extend radially outwardly of the hydrocyclone chamber outer wall, the diameter of the outer wall must be decreased to enable the hydrocyclone and its connections to fit within the pipe. The diameter of the outer wall can be reduced only a limited amount if adequate flow within the cyclone is to be achieved.
In addition, there are some drilling operations in which the drilling is vertical at the beginning and then is horizontal or close to horizontal. In such cases, there is a curved transition portion between the vertical and horizontal portions which may, for example, have a radius of about forty feet. If the hydrocyclone is to be positioned in the horizontal portion of the well bore, the exterior dimension of the hydrocyclone and its connections and the length of the hydrocyclone must be selected so that the combination can be fed through the curved transition portion. Accordingly, it is desirable to keep such exterior dimension to a minimum.
A hydrocyclone requires an inlet connection for the input stream and at least one outlet connection for a separated constituent is required. When the apparatus is installed in a hole, a conduit, such as a flexible hose, is required from the outlet to a point above ground. In some prior art hydrocyclones, the inlet connection extends radially from the apparatus to permit directing the stream tangentially to the chamber walls. Also, in the prior art, the outlet connection may extend radially from the apparatus. Both such radially extending connections can undesirably restrict the maximum diameter of the chamber for a given hole size.
It has been proposed that the inlets and outlets of a hydrocyclone be located substantially within, or within, a projection of the periphery of the chamber so that the apparatus has substantially the same outer size throughout its length. See, for example, U.S. Pat. Nos. 2,147,671 and 5,431,228.
In the apparatus in U.S. Pat. No. 2,147,671 in which the inlet connection is substantially within a projection of the periphery of the outer wall of the chamber (FIG. 5), the cylindrical stream directly impinges on the helical plate and is not directed at the angle of the helical plate, i.e. the stream is directed at an angle to the plate. There is no transition region between the stream inlet and the helical plate. As a result, the sudden change in stream path will cause undesirable disturbances in the stream which may persist for several turns of the helical path. A smooth transition from the inlet to the helical path is very important for establishing fully developed and desired flow at or near the beginning of the helical path to increase the useful portion of the hydrocyclone.
Although U.S. Pat. No. 5,431,228 shows hydrocyclone inlets and outlets within the projection of the outer wall of the cyclone chamber, the connections to the inlet and outlet are above ground so that it is not necessary that the connections fit within the well pipe and the connections are not so described. In addition, the inlet of the hydrocyclone is of the same size as the diameter of the outer wall of the cyclone and is coaxial with the cyclone helix. Also, the distance between the inner side of the chamber outer wall and the periphery of the helix support rod is relatively large.